Reference · Eastern Idaho
Two published sets of numbers exist for this area and they disagree, sometimes by more than double. This page shows both, and states plainly which one you have to build to.
Mon–Fri 8am–5pm · Idaho Falls and the surrounding towns
Send the address and the size you have in mind. You’ll get the design load your jurisdiction requires and the office that permits it.
Read this before the table
The City of Idaho Falls requires a 47 psf ground snow load. That figure traces to the 1986 edition of the Idaho snow load study. The 2015 University of Idaho update calculated 23 psf for the same location.
Both numbers are real and both are published. Only one of them gets a permit stamped. The adopted number governs. A truss package engineered to 23 psf inside Idaho Falls city limits is a building that does not comply, no matter which study you point at.
Nobody should read this page and design to a lower figure than their jurisdiction requires. The 2015 column below is context for why bids differ between towns — it is not a permit input unless your jurisdiction has adopted it.
Sort by town, elevation or the 2015 value. The 1986 column is shown because that edition is the lineage behind several figures still in force locally. Where the 1986 edition lists no value for a town, the cell reads as a dash rather than a guess.
| Pg (1986) | |||
|---|---|---|---|
| Blackfoot | 4,498 ft | 28 psf | 23 psf |
| Firth | 4,567 ft | 44 psf | 22 psf |
| Basalt | 4,592 ft | 45 psf | 55 psf |
| Shelley | 4,629 ft | 35 psf | 49 psf |
| Ammon | 4,718 ft | 24 psf | 50 psf |
| Idaho Falls | 4,725 ft | 23 psf | 47 psf |
| Roberts | 4,777 ft | 33 psf | 32 psf |
| Iona | 4,783 ft | 23 psf | 49 psf |
| Menan | 4,803 ft | 30 psf | 37 psf |
| Ucon | 4,807 ft | 25 psf | 43 psf |
| Rigby | 4,851 ft | 32 psf | 41 psf |
| Ririe | 4,963 ft | 59 psf | — |
Source: Ground Snow Loads for Idaho, 2015 Edition (Al Hatailah, Godfrey, Nielsen and Sack, University of Idaho), with the 1986 edition shown for comparison.
Bingham County publishes the ground snow load for unincorporated parcels as an equation driven by elevation. Bingham County Code Title 8, §8-1-2-1 states it as “elevation in feet above mean sea level divided by 100, minus 5 equals the ground snow load. (Elevation/100-5 = Pg)”
Published formula — Bingham County Code Title 8, §8-1-2-1
Ground snow load = (elevation ÷ 100) − 5
Because the elevation term is divided by 100 before the subtraction, the load climbs roughly one pound per square foot for every hundred feet you gain. Two parcels on the same road at different bench heights do not carry the same number.
Run it on Blackfoot and the binding-number rule shows up again: the county’s adopted formula gives 40 psf, while the 2015 University of Idaho study calculated 28 psf for the same town. The adopted number is the higher one, and the adopted number is the one your permit is judged against.
Run your own parcel elevation through the same three steps, then confirm the result with Bingham County Planning and Development at (208) 782-3177 before anything is ordered. The formula is the county’s; the arithmetic above is just the formula applied.
A truss order needs more than a psf figure. These are the other adopted design criteria published for the two jurisdictions that publish them.
Criteria for other jurisdictions on this list are not published in a comparable sheet. Where a figure is not published, call the office rather than assume the neighboring county’s number applies. Who permits what →
Two published datapoints exist. They measure different things, so read them as a pair rather than a range.
Broad estimate
$5,000–$20,000+
Steel Structures America states that engineering for Idaho and Montana loads “can add $5,000 to $20,000 or more on a mid-size building.” That is a whole-building statement: heavier trusses, more posts, more steel, more connections — not a plan-set fee.
Documented single case
$1,580
Hansen Pole Buildings documented raising a design from 60 psf to 75 psf ground snow along with a 25% wind increase at a $1,580 up-charge including new sealed plans and truss drawings. One building, one specific step up — narrower and harder than the range above.
Neither figure is a quote for your building, and no source publishes a per-psf price for this area. What both establish is direction: the design load is a cost driver you decide once, at the drawing stage, and cannot cheaply revisit after material is ordered. Full cost breakdown →
A flat balanced load across an open roof is the easy case. Add a lean-to and you create a step in the roofline — a lower roof running into a taller wall. Snow does not stay evenly spread across a step. Wind moves it off the upper roof and it piles against the wall, so the lower roof near that junction carries a surcharge well above the balanced ground snow figure.
This is why an added bay is not simply “more of the same roof.” The lean-to itself has to be designed for the drift, and in some cases the existing structure at the junction has to be checked too. It is the single most common place an addition turns out to need engineering the owner did not budget for.
The effect scales with the height of the step and the length of the upper roof feeding it. In a 47 psf jurisdiction, a drift surcharge on top of that starting point is a serious number, and it is not one to eyeball.
If any of these describe your project, the design load conversation happens before the layout is finalised, not after.
Source of the 2015 column in the table above, and of the 23 psf calculation for Idaho Falls.
Source of the adopted 47 psf ground snow load, 30-inch frost line, 115 mph ultimate wind and Seismic Design Category D.
Source of the elevation formula and the county wind and seismic criteria.
Adopted criteria change. Everything on this page should be confirmed with the office that will issue your permit before it is used for design.
Send the address and the size you have in mind. You'll get the office that permits it, the ground snow load in force there, and what that load means for the truss package.